String-shaped product with connecting and/or fixing means

ABSTRACT

An electric cable is configured as a sensor cable, wherein the lead insulation of the cable has a polymer layer. The sensor cable can be produced by, after extruding the raw cable, cutting the cable into individual cable sections in a non-crosslinked state. The sections are then connected to a sensor in an electrically conductive manner. The housing of the sensor consists of a plastic material that is compatible with the lead insulation and that is radiation crosslinkable. The polymers of the lead insulation and the polymers of the sensor housing are crosslinkable with themselves and with one another. A compatibilizer or a reactive terpolymer enabling connection of functional groups between the layers can also be added to the lead insulation and/or the plastic housing. The plastic materials of the lead insulation and the sensor housing are crosslinked in a separate crosslinking process under the effect of high-energy electron radiation.

TECHNICAL BACKGROUND

The invention concerns string-shaped or tape-shaped extruded linearproducts that incorporate at their ends thermoplastic end pieces orfixing means, whereby the thermoplastic end pieces or fixing means areradiation crosslinked together with the linear product duringproduction.

The invention further concerns a method that is especially suited forthe production of such a product.

Electric cables with welded or moulded connecting means are an exampleof such string-shaped products.

Electric cables according to this invention are for example equippedwith a sensor means for measuring the rotation speed of a motor, gears,or a wheel at one end and incorporate an insulation, which is resistantagainst liquid, steam, or gaseous media depending on the use, and whichmay possibly include high resistance against mechanical wear.

PRIOR ART

Sensor cables of this type are for example used within the automotiveindustry, as well as the rail, aircraft and spacecraft industries. Thesensor cables must satisfy special requirements especially for theseapplications and incorporate lead insulation with specialcharacteristics. Amongst others the latter must therefore be

-   -   oil resistant and resistant against various chemicals,    -   flame resistant and environmentally friendly,    -   temperature and friction resistant as well as    -   mechanically robust    -   resistant against ageing and reliable    -   flexible and environmentally resistant.

The interface via which the sensor means is connected to the cable mustalso satisfy these requirements at least in part.

For the production of insulated electric cables which produce a minimumof smoke in case of fire as well as no and/or only very small quantitiesof toxic gas, a halogen-free insulation material is used today, such asfor example polyethylene, ethylene copolymers, and other polymers thatcan be irradiated.

The flame resistance of a halogen-free insulation material is—as isalready known—achieved with an addition of aluminium trihydrate (ATH)and/or magnesium hydroxide. Electric cables with halogen-free insulationthat incorporate such hydrates are known to suffer from the disadvantageof a reduced resistance against liquid media such as for example petrol,mineral oils, and organic solvents. In order to overcome thisdisadvantage the electric cables are equipped with a two-layer leadinsulation, which in turn consists of a halogen-free inner insulationlayer made from a flame resistant polymer, for examplepolyolefin-copolymer, and an outer protective layer made from apolyamide, a thermoplastic, halogen-free polyester elastomer, or ahalogen-free, aromatic polyether. During the production of such electriccables polar polymers with oil-repellent characteristics are thereforeselected for the chemically resistant outer layer. For the inner layer,however, plastics with good absorption characteristics for flameprotection materials are available.

For the production of sensor cables, the electric cable and the sensor,which in turn consist of an electronic component containing a housingconstructed from metal or plastic, are currently produced at separateindustrial facilities and subsequently assembled at one of the twofacilities or at a separate third facility to form the sensor cables.The cable sections intended for the production of the sensor cables areunwound from cable rolls, cut, and connected with the sensor during aseparate working step, whereby the cable is first electricallyconductively connected with the electronic component of the sensor,whereafter the sensor housing made of metal or plastic is affixed to theelectronic component and welded or moulded to the cable sleeve.

A substantial disadvantage of this known process for the production ofsensor cables consists of the fact that the two main components of theknown sensor cable incorporate some physical characteristics thatprevent an optimal connection of the lead insulation with the sensorhousing. The plastic composition of the lead insulation with thematerial of the sensor housing is therefore not optimally compatible,even when the sensor housing also consists of plastic. This results inthe fact that the preferably radiation crosslinked insulation layer ofthe electric cable adheres very poorly to the sensor housing, so thatthe oil and temperature resistance, as well as the mechanicalrobustness, and especially the extraction force, is limited far morethan desired. Known products also often show weaknesses when largetemperature fluctuations occur and struggle to maintain theircharacteristics over extended time periods.

BRIEF SUMMARY OF THE INVENTION

It is the purpose of this invention to provide a novel electric cablewith connecting means, especially a sensor cable of the type mentionedabove, that does not incorporate the above mentioned disadvantages, andthat is especially relatively easy to produce thanks to a logisticallyadapted method. The method shall be especially suitable also for theproduction of any other string-shaped products such as for exampleplastic pipes, plastic hoses, foils and foil laminate.

This task is solved in accordance with the invention by a string-shapedproduct, for example an electric cable, with the characteristicsdescribed below.

Preferred embodiments of the electric cable of this invention and themethod of this invention are described below.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 illustrates one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one preferred embodiment of the invention the cable takes the form ofa sensor cable, i.e. sensor line, and the lead insulation consists alsoof a flame resistant and halogen-free, radiation crosslinkable polymerlayer, which in turn contains a polyamide, a polyolefin, or a polyolefinblend. Depending on the type and application of the string-shapedproduct, all radiation crosslinkable plastics are suitable for therealisation of the invention, whereby halogen-containing plastics areespecially suitable for higher temperatures, if this is an advantage,for example fluor-containing polymers.

In comparison, the sensor of the known type consists of an electriccomponent and a housing containing the electric component, the housingbeing made from plastic. According to the present invention, the housingconsists of a plastic or plastic mixture that is compatible with thelead insulation and is radiation crosslinkable, containing for exampleat least one polyamide and/or a polyolefin, such as polyethylene. Thepolymers of the lead insulation and the polymers of the sensor housingare preferably selected in such a way that they can be moulded togetherin their assembled, but non-crosslinked state.

The sensor cable can be produced in this case as follows:

-   -   Following the extrusion of the preferably non-crosslinked or        only partially crosslinked raw lead, the lead is cut into        individual cable sections which are then electrically        conductively connected with a sensor at their ends in the known        way.    -   Subsequently the plastic of the lead insulation and that of the        sensor housing, connected with one another in their pre-produced        form of the cable at least in part, for example moulded        together, are crosslinked during a separate crosslinking process        under the influence of energy-rich electron radiation (electron        beam radiation). This will result in a connection of the        polymers of the lead insulation with those of the sensor housing        to form one polymer network, so that a predominantly        mechanically resistant cable construction is created in this        way.

In a further embodiment of the sensor cable described above, as shown inFIG. 1, the lead insulation of the cable 10 consists of a co-extrudant,for example consisting of a flame resistant, halogen-free inner polymerlayer 14 and a chemically resistant, oil resistant, outer polymer layer13, which is especially adherent to, (i.e. connected with) the same andcompatible with the same, and which possibly also contains additionalflame protection material. In this embodiment the inner layer 14incorporates at least one polyolefin or polyolefin blend, and the outerlayer 13 incorporates a polyester elastomer and/or a polyamide and/or apolyethylene, such as for example a high density polyethylene (HDPE). Inaddition the outer layer 13 is also formed in such a way and adapted tothe plastic composition of the sensor housing 11, that the outer layer13 can be moulded to the sensor housing 11 and radiation crosslinked inthe way described above. The outer layer 13 therefore normally consistsof an extrudable plastic that can be crosslinked.

For the production of electric cables 10, the raw cable is therefore cutinto individual sections in this case also, which are then connected toa sensor at their ends, for example by molding. Following this at leastthe polymers of the outer layer 13 of the lead insulation and thepolymers of the sensor housing 11 are treated under the influence ofenergy-rich electron radiation (electron beam radiation) in such a waythat the outer layer 13 and the sensor housing 11 crosslink to form onesingle polymer network 12.

Yet another embodiment of an electric cable 10 according to thisinvention consists of several electric leads interwoven with oneanother.

Such a cable is equipped with a one or two-layer sleeve and can beproduced as follows.

On a copper braid, itself consisting of a multitude of individual wires15 with a total cross-section of 0.13 mm² to 16 mm² a normally radiationcrosslinkable insulation layer is first applied. Two or more suchinsulated leads are then, usually following an interweaving process,coated with an outer sleeve 13 layer through co-extrusion, for which tworaw materials preferably belonging to the previously mentionedconnection classes for the inner, and outer layer 14, 13 of a leadinsulation and intended for the formation of the inner and outer sleevelayers 14, 13 are supplied.

The inner material layer 14 is preferably produced with a thickness of0.1 to 2 mm, more preferably 0.2 to 1.5 mm, whilst the layer thicknessof the outer layer 13 can be relatively thin and generally consists ofapproximately 0.05 to 0.5 mm. If the outer layer 13 does not contain aflame protection material, the flame resistant characteristics of theentire lead insulation are provided by the inner layer 14. Accordinglyit is important that the volume ratio, (i.e. the layer thickness ratioof the two layers) is matched.

Due to their polymer composition, both layers of the cable sleeveincorporate robust mechanical characteristics. In particular, the innerlayer 14 thus incorporates a high tensile strength and high expansioncapabilities, and the outer layer 13 incorporates a high frictionresistance.

Whilst the outer layer 13 incorporates at least one polyester elastomerand/or a mechanically robust polymer and is selected primarily so thatits plastic composition can be moulded to and crosslinked with thehousing 11 of the connecting means, for example the sensor, the innerlayer 14 can be formed differently depending on the application, forexample with good absorption characteristics for flame protectionmaterial.

For the production of electric cables, the raw cable is cut intoindividual cable sections in this case also, which are then connected toa sensor at their ends, whereby this results especially in theconnection, and possibly the moulding of the sensor housing 11 and outersleeve layer 13. Following this, at least the polymers of the outersleeve layer 13 and the polymers of the sensor housing 11 are treatedunder the influence of energy-rich electron radiation (electron beamradiation) in such a way that the outer sleeve layer 13 and the sensorhousing 11 crosslink to form a single polymer network 12.

The overall characteristics profile of the double-layer lead insulationor the possibly present double-layer cable sleeve is provided by a taskdistribution between the two layers of the insulation.

Suitable polyolefins for the formation of the single layer lead, thesingle layer sleeve, or the outer lead, (i.e. sleeve layer) according tothe invention are the following polymer groups:

-   -   polyamides (PA)    -   polybutyleneterphthalate (PBTP)    -   polyethyleneterephtalate (PETP)    -   polyethylene copolymers, such as for example        ethylene-vinyl-acetate (EVA), ethylene-methylacrylate (EMA),        ethylene-butylacrylate (EBA)    -   EEA; EPDM; PE-C; PP;    -   polyethylene homopolymers;    -   maleic acid anhydride (MAH)-terpolymers;    -   glycidylmethacrylate (GMA)-terpolymers; polyvinylchloride;        styrolpolymers; ABS; BS; PS halogenated polymers; CSM; ETFE;        PEP; FPM; PE-C; PVC; PVDF; PVF;    -   elastomers and thermoplastic elastomers.

According to the invention the polymers of the inner lead and outer leadlayer, i.e. the inner sleeve 14 and the outer sleeve layer 13 areselected in such a way that the inner sleeve 14 and the outer sleeve 13adhere to one another, (i.e. are connected with one another) in theirapplied, co-extruded condition, so that the mechanical frictionresistance of the lead insulation is increased. In order to furtherincrease adhesion between the two layers, the at least one polymer ofthe inner layer 14 and/or the at least one polymer of the outer layer 13can be equipped with an additional compatibilizer (for example a blockpolymer) or a reactive terpolymer, to enable a connection of functionalgroups between the layers.

Main characteristics of the possibly present outer lead or sleeve layers(as opposed to the total layer when the lead insulation or sleeveconsists of one layer) for the connecting of the outer layer 13 with thesensor housing 11 according to the invention are the mouldability andcrosslinkability of the outer layer 13 with the plastic of the sensorhousing 11, i.e. the material composition of the relevant layers isdetermined by the sensor housing 11.

The choice of material for use with this invention is thereforeaccording to the following sequence:

-   1. For the sensor housing 11 a heat-stable, crosslinkable, and    possibly mouldable plastic should be chosen.-   2. The cable enclosure should be chosen in such a way that the outer    layer 13 can be thermoplastically moulded to and crosslinked with    the relevant plastic of the sensor housing 11.

As already mentioned above at least the outer layer 13 of the leadinsulation, (i.e. the cable sleeve) is radiation crosslinked with thesensor housing 11 in the end product of this invention. If one alsowants to crosslink the relevant inner layer 14 in this particularembodiment the outer layer 13 raw material must possibly be additionallyequipped with low molecular crosslinking enhancers.

The sensor cable of this invention has the following physicalcharacteristics:

-   -   It incorporates a high mechanical firmness, especially within        the area of the cut between cable and sensor means, which is due        amongst others to the moulding together and crosslinking of lead        insulation, i.e. the sleeve and sensor housing. The sensor cable        is tight and resistant to ageing across a wide temperature range        without additional auxiliary elements.    -   Flame resistance tests are passed successfully by the        double-layer lead insulation, i.e. sleeve insulation.    -   The sensor cable of this invention with its double-layer lead        insulation is not only oil resistant. It is also resistant        against other liquids, chemicals, and steam, such as for example        antifreeze, battery fluid, windscreen washer fluid, brake fluid,        detergents, motor and gearbox as well as hydraulic fluids and        petrol.    -   It can be used without problems especially within the automotive        industry, and more specifically in connection with sensors for        the measuring of rotation speed, torque, pressure, oxygen        content, temperature, oil level, air quality, etc.

Finally it should be said that the above mentioned embodiments representonly a selection of several possible embodiments of the invention, andthat the invention can be varied and amended in many different ways. Itis therefore possible to crosslink the ends of entire cable harnesses asa single component set during one working step instead of individualsensor cables. Such cable harnesses are often used within the automotiveindustry and consist for example of several interconnected cablesections.

It is further possible in line with the method of this invention toproduce plastic pipes and hoses with welded coupling sectionscrosslinked with the pipe, i.e. the hose as well as foils and laminateswith welded and crosslinked folds and edge areas. In this case also thestring-shaped products produced according to the invention incorporateimproved characteristics with regard to temperature resistance, frictionresistance, sealing, and tear resistance. Finally the method of thisinvention can also be used with suitable plastic compositions toreinforce, i.e. freeze the shape and/or structure of a component, forexample the shape of a coiled cable, which in turn consists at least inpart of radiation crosslinkable components, during a final process stepby crosslinking. This shape will then be maintained even at highoperating temperatures.

1. An electrical cable comprising: an electrical conductor; an exteriorinsulation layer surrounding said electrical conductor; and a connectorhaving a plastic housing welded together with said exterior insulationlayer and crosslinked together with said exterior insulation layer byenergy rich electron beam radiation so as to form a single polymernetwork.
 2. The electrical cable of claim 1, wherein said exteriorinsulation layer includes a halogen-free, crosslinkable polymer layerwhich includes a polyamide, a polyolefin or a polyolefin blend.
 3. Theelectrical cable of claim 1, wherein said exterior insulation layerincludes a flame resistant, halogen-free, crosslinkable polymer layerwhich includes a polyamide, a polyolefin or a polyolefin blend.
 4. Theelectrical cable of claim 1, wherein said plastic housing includes aplastic that is compatible and crosslinkable with said exteriorinsulation layer, and includes at least a polyamide, a polyolefin or apolyethylene.
 5. The electrical cable of claim 1, further comprising aplurality of electrical conductors, including said electrical conductor,each of said electrical conductors being surrounded by a respectiveinterior insulation layer, said plurality of electrical conductors andsaid interior insulation layers being surrounded by said exteriorinsulation layer.
 6. The electrical cable of claim 5, wherein each ofsaid interior insulation layers includes a flame resistant, halogen-freepolymer layer including at least one polyolefin or polyolefin blend, andsaid exterior insulation layer includes a chemical resistant, oilresistant polymer layer including at least one polyester elastomer, apolyamide or a polyethylene.
 7. The electrical cable of claim 5, whereineach of said interior insulation layers includes a flame resistant,halogen-free polymer layer including at least one polyolefin orpolyolefin blend, and said exterior insulation layer includes a flameresistant, chemical resistant, oil resistant polymer layer including atleast one polyester elastomer, a polyamide or a polyethylene.
 8. Theelectrical cable of claim 5, wherein each of said interior insulationlayers is crosslinked together with said exterior insulation layer.
 9. Amethod for producing an electrical cable, the method comprising:surrounding an electrical conductor with an exterior insulation layer;welding the exterior insulation layer together with a plastic housing ofa connector; and crosslinking the exterior insulation layer togetherwith the plastic housing by energy rich electron beam radiation so as toform a single polymer network.
 10. The method of claim 9, wherein theexterior insulation layer includes a halogen-free, crosslinkable polymerlayer which includes a polyamide, a polyolefin or a polyolefin blend.11. The method of claim 9, wherein the exterior insulation layerincludes a flame resistant, halogen-free, crosslinkable polymer layerwhich includes a polyamide, a polyolefin or a polyolefin blend.
 12. Themethod of claim 9, wherein the plastic housing includes a plastic thatis compatible and crosslinkable with the exterior insulation layer, andincludes at least a polyamide, a polyolefin or a polyethylene.
 13. Amethod for producing an electrical cable, the method comprising:surrounding each electrical conductor in a plurality of electricalconductors with a respective interior insulation layer; surrounding theplurality of electrical conductors and the interior insulation layerswith an exterior insulation layer; welding the exterior insulation layertogether with a plastic housing of a connector; and crosslinking theexterior insulation layer together with the plastic housing by energyrich electron beam radiation so as to form a single polymer network. 14.The method of claim 13, wherein each of the interior insulation layersincludes a flame resistant, halogen-free polymer layer including atleast one polyolefin or polyolefin blend, and the exterior insulationlayer includes a chemical resistant, oil resistant polymer layerincluding at least one polyester elastomer, a polyamide or apolyethylene.
 15. The method of claim 13, wherein each of the interiorinsulation layers includes a flame resistant, halogen-free polymer layerincluding at least one polyolefin or polyolefin blend, and the exteriorinsulation layer includes a flame resistant, chemical resistant, oilresistant polymer layer including at least one polyester elastomer, apolyamide or a polyethylene.
 16. The method of claim 13, furthercomprising: crosslinking each of the interior insulation layers togetherwith the exterior insulation layer.